We propose a scheme for realizing quantum three-qubit phase gate operation, in a three-mode cavity where the large detuned cavity-mode fields interact with the four-level artificial atom of an rf-SQUID in tripod-type configuration. In this scheme, the two lowest levels of the artificial atom represent the two logical states of the target qubit and two cavity-mode states are the control qubits, while the third cavity-mode field serves the gate manipulation. Since only the metastable lower levels are involved in the gate operations, the gate is insensitive to the decay rates of the artificial atom, which makes this scheme advantageous and it is important in view of decoherence.
rf-SQUID measurements of anomalous Josephson effect